Anatomical mapping systems provide the three-dimensional (3D) position of a navigational catheter within the cardiac chamber of interest and, in some instances, can also be used to construct 3D maps of the cardiac chamber. Systems such as CARTO (Biosense Webster, Diamond Bar, Calif.) use the electromagnetic position of the catheter tip relative to an electromagnetic locator pad which is placed below the patient and a reference catheter at a fixed external (usually posterior) location. LocaLisa (Medtronic, Minneapolis) and NavX (St. Jude's Medical, Minneapolis, Minn.) systems use voltage gradients generated by external electrical fields to spatially orient and localize the catheter tip. The EnSite system (St. Jude's Medical) uses an electrically-coded catheter and a multi-electrode mapping balloon to create maps and define the location of the navigational catheter. The CARTO, Ensite, LocaLisa, and NavX systems have been used to create 3D maps of the left atrium (LA) and will be described in more detail.
The CARTO system provides electroanatomic mapping based upon the premise that an electrical current is generated when a metallic coil is placed in a magnetic field. The magnitude of the current depends on the strength of the magnetic field and the orientation of the coil in the field. The CARTO system consists of a magnetic field emitter mounted under the patient, a location sensor inside the mapping and ablation catheter tips, and a data processing unit and graphical display unit to generate and display the 3D model of the cardiac chamber of interest. Data on the amplitude, frequency, and phase of the magnetic field are gathered and analyzed by the processing unit and displayed on the display unit. The CARTO mapping system uses a triangulation algorithm in which a sensor in the catheter tip allows the determination of its distance from each coil. In addition to the x, y, and z coordinates of the catheter tip, the CARTO mapping system can determine three orientation determinants—roll, yaw, and pitch. The position and orientation of the catheter tip can be seen on the screen and monitored in real time as it moves within the electroanatomic model of the chamber being mapped.
Since the CARTO mapping system is not an imaging technique, fluoroscopy is initially used to establish orientation by using generally known anatomic locations in the heart as references for the later creation of the model of the mapped chamber. An electromagnetic anatomical reference patch is placed on the back of the patient and is used to track the mapping and ablation catheter. For activation mapping, an electrical reference such as an ECG signal or an intracardiac recording is used. For intracardiac recordings, coronary sinus recordings are often selected because they are usually stable. For activation, points taken by the catheter are color-coded orange, yellow, green, blue and purple for progressively-delayed activation areas. Similarly, the voltage map is also color-coded and superimposed on the anatomic model. Using these techniques, both the mechanism of the arrhythmia and the 3D anatomy can be created. However, creation of an electroanatomic map may be a lengthy process involving the tagging of many points, depending upon the spatial details needed to analyze a given arrhythmia. Lack of accurate ECG and respiration gating and non-real-time data are other limitations of this technique. Furthermore, the catheters used are very expensive and fluoroscopy is always used as a backup to identify the location of catheters.
Non-contact mapping using the EnSite system is based upon the premise that endocardial activation creates a chamber voltage field which obeys LaPlace's equation. The EnSite system includes of a multi-electrode balloon which is placed inside the heart chamber of interest. The balloon or multi-electrode array is comprised of a braid of 64 polyamide-insulated, 0.003 mm diameter wires. For electrophysiologic studies, any mapping catheter can be used. The catheter location system uses a low-level, 5.68 kHz current emitted by a distal electrode which returns to each of two intrachamber ring electrodes on the multi-electrode array. Since the position of both the array electrodes and the current sink electrodes are known, a custom algorithm determines the position of the roving catheter by demodulating the 5.68 kHz potentials. The mapping catheter is moved around the chamber to create a 3D map. A high-resolution activation and 3D map can be created using custom-built algorithms. The EnSite system, like the CARTO system, has been used to treat arrhythmias including atrial fibrillation, atrial flutter, atrial tachycardias and ventricular tachycardias. Again, like the CARTO system, the EnSite system is very expensive, its resolution depends on the number of points taken, and a fluoroscopic system is commonly used to confirm the location of catheters.
The LocaLisa system uses 1 mA-current-generated electromagnetic fields at approximately 30 kHz, emitted from cutaneous patches placed on the subject's chest. These patches are positioned to create a 3D axis system. In addition to the connection of the position reference catheter and a mapping-ablation catheter, the LocaLisa system provides several other channels on which recordings can be made from several different catheters. Catheters in the subject's heart receive these signals, and the position of the catheter can be determined. One limitation of the LocaLisa system is that it merely provides the user with information about the catheter position—no geometric anatomical model can be created.
The NavX system, in addition to having all of the features of the LocaLisa system, can also, similar to the CARTO system, create activation maps and 3D anatomical maps of the chamber of interest. As described above, these technologies have several limitations. As in other electroanatomic mapping systems, the accuracy of the chamber reconstruction process is directly dependent upon the number of the points taken and the position of the catheter. Another significant limitation is that the heart is essentially considered a rigid body over which maps such as activation map are displayed. Also, cardiac chamber distortion due to cardiac and respiratory motion is not taken into account if a significant change in heart rate occurs from the time the map was created to the time therapy is delivered. However, the biggest drawback, as described before, is that these systems are expensive, require separate mapping systems, and do not provide real-time visualization of the chamber. Consequently, fluoroscopy is used almost all the time to confirm location of the system.
Fluoroscopy is used in all cardiac labs to identify location of catheters and other interventional instruments such as leads, stents, or other instruments. However, in the past, fluoroscopy has not been used to create 3D maps since it provides only two-dimensional images. Furthermore, unlike anatomical systems described before, anatomical maps, electrical maps and voltage maps cannot be created by currently-available fluoroscopy systems.
This invention resolves these issues by providing a system which creates a 3D model using only single-plane fluoroscopic images and a catheter as it is moved around the heart chamber of interest. Furthermore, activation maps, electrical maps and voltage maps can be created on this 3D model, and the location of catheter marked as needed.
Fluoroscopy is used to visualize body organs and structures such as bones. Since it is available in all labs to navigate catheters, sheaths, and the like, the present invention uses this imaging technique to create 3D maps which in the past have not been created due to two-dimensional modality of the fluoroscopy imaging system. In a fluoroscopic system, the X-ray generator allows selection of the voltage and current delivered to the X-ray tube. Two methods, continuous and pulsed exposure, are used for fluoroscopy. During continuous fluoroscopy, the generator provides steady tube current. Images are usually acquired at a rate of 30 frames per second, resulting in an acquisition time of 33 milliseconds (msec) per image. During pulsed fluoroscopy, for example, a frame rate such as 30 frames per second may be used with each exposure having a short duration of 3 to 10 msec. Thus, heart-cycle-gated fluoroscopy imaging may, for example, use pulses of 3 to 10 msec in duration only at predetermined phase (such as diastole), thus improving the resolution and reducing radiation exposure.